Liquid desiccant vapor separation system

Abstract

An atmospheric moisture harvesting system, in which water vapor is separated from the air using a liquid desiccant subsystem. The moisture charged liquid desiccant enters a desorber and condensation system, where the moisture is extracted. Cooling and condensation are performed on the extracted water vapor only, thereby saving the energy for cooling air containing the water vapor, as is done in direct cooling systems. The system thus operates as a single stage vapor separation system since the vapor concentration remains in the liquid desiccant which is circulated to the separation and condensation subsystems without air laden with the moisture. Low grade or solar heat can be used as the energy source for the vapor desorption. A heat exchanger utilizes unwanted heat from regenerated desiccant to heat up charged desiccant entering the regenerating stage. The system has substantial energy savings over prior art systems using direct cooling of air.

The invention claimed is: 
     
       1. A method of extracting water from atmospheric air, comprising the steps of:
 charging liquid desiccant having a concentration below supersaturation, with water vapor from said atmospheric air in contact with said liquid desiccant flowing along a surface in an absorber vessel; 
 desorbing said water vapor by heating said charged liquid desiccant in a flash drum desorbing vessel at a sub-atmospheric pressure; 
 cooling said water vapor to a temperature below 20° C. such that water is condensed therefrom; and 
 returning said heated desorbed liquid desiccant to said absorber vessel through a heat exchanger, in which at least part of its heat content is transferred to said charged liquid desiccant passing from said absorber vessel to said flash drum desorbing vessel. 
 
     
     
       2. The method according to  claim 1 , wherein said desorbing of said water vapor is performed on a part of said liquid desiccant charged with water vapor, such that the other part of said liquid desiccant can be recirculated through said absorber vessel to be further charged with water vapor in said absorber vessel. 
     
     
       3. The method according to  claim 1 , wherein said heating said charged liquid desiccant in said flash drum desorbing vessel at said sub-atmospheric pressure is performed using heat from a low grade or solar heat source. 
     
     
       4. The method according to  claim 1 , wherein said condensed water is collected from said vapor condenser through a barometric leg into a storage vessel. 
     
     
       5. The method according to  claim 1 , wherein said heated desorbed liquid desiccant from said flash drum desorbing vessel is returned to said absorber vessel through a barometric leg. 
     
     
       6. The method according to  claim 1 , wherein said sub-atmospheric pressure in said flash drum desorbing vessel is maintained by use of a vacuum pump. 
     
     
       7. The method according to  claim 6 , wherein said vacuum pump is connected to said flash drum desorbing vessel through said vapor condenser.